Food safety is a consumer issue of long standing. Even if a particular item was fresh at the time of its transportation to the point of sale or even at the time the end user obtains it, its freshness and safety at the actual time of use cannot be guaranteed. Thus, a method that would enable the end user to check a foodstuff for contamination immediately prior to consumption would be of major benefit to the consumer. Non-invasive methods, i.e. methods that do not involve removal or destruction of a portion of the food being tested, would be ideal, since such a method would provide ease of use and hence a higher likelihood of use.
Spectroscopic methods for determination of food safety meet the requirements of being non-invasive and of being easy in principle to use. There are two major obstacles that need to be overcome before use of such methods by the end user can become routine. The first is the necessity to provide an appropriate spectrometer. FIG. 1 shows a design of a typical spectrometer 10 known in the art. Light 105 enters through slit 100, is reflected from first mirror 101 onto a dispersive element such as a grating (103) which directs the light onto a second mirror 102. Because the light is dispersed by element 103 according to its wavelength, every pixel of the spectrometer's sensor 104 will be illuminated by a specific wavelength. Spectrometers that use this design are complicated, require precise alignment, are difficult to assemble and are limited in their miniaturization capabilities.
In contrast, a spectrometer suitable for routine consumer use must be small, rugged, easy to use, and capable of providing spectra of sufficient quality and resolution that meaningful conclusions about the content of the food being tested can be made. The second obstacle is that foods and their contaminants are in general not simple substances, but complex mixtures of substances that themselves tend to have complicated spectra. Thus, for such an end-user system to be useful, it must incorporate means for real-time analysis of the frequently complicated spectra obtained.
While development of such a spectrometry system would be a boon to end-user determination of food safety, its usefulness would extend far beyond such a limited use. For example, it could be used in applications as diverse as detection of environmental contaminants, remote detection of explosives or chemical or biological agents, or for remote diagnosis or monitoring of a patient's condition (e.g. blood oxygen or glucose levels).
There has thus been a considerable effort devoted to development of compact spectrometry systems to meet these needs. Some examples of compact spectrometry systems known in the art are given here.
U.S. Pat. No. 7,262,839 discloses a compact birefringent interference imaging spectrometer. This spectrometer comprises at least one liquid crystal cell or a micromechanical Fabry-Perot system that is used as a tunable filter. In some embodiments, the liquid crystal cell can be designed to create a series of bandpass zones. Different wavelengths are tuned across the x-y image field of a two-dimensional detector, enabling collection of wavelength resolved or spatially resolved spectral data.
U.S. Pat. No. 7,420,663 discloses a portable spectroscopic sensing device that is integrated into a mobile communication device such as a mobile telephone. The spectrometer uses the sensor associated with the camera located in the mobile communication device as a detector, and its connection with the mobile device allows uploading of the spectral information thus obtained to a remote location. The spectroscopic sensing device disclosed is based on a dispersive element such as a grating or prism, with all of the consequent drawbacks of such a device.
U.S. Pat. Appl. 2010/0201979 discloses a system and method for performing spectral-spatial mapping. Instead of a dispersive element such as a prism or grating, the system disclosed therein uses a cylindrical beam volume hologram (CVBH) to disperse the light. This design has the advantage that no slit or grating is needed, but suffers from drawbacks of low throughput and small spectral range. In addition, the expense of the CVBH element precludes its use in a spectrometer intended for consumers.
U.S. Pat. Appl. 2010/0309454 discloses a portable spectrometer integrated into a wireless communication device. Not only does the spectrometer disclosed therein depend on dispersive elements, but the system itself requires the use of a fiber optic cable attached to the wireless communication device to transmit light to the spectrometer, further limiting the ease of use and increasing the cost of the system.
Thus, a compact spectrometer system that can be integrated into a consumer device such as a cellular telephone while being sufficiently rugged and low in cost to be practical for end-user spectroscopic measurements of suspect items, and a convenient method by which the spectra obtained by such a spectrometer system (in particular those of complicated mixtures such as foodstuffs) can be analyzed and the likelihood of contamination estimated remains a long-felt yet unmet need.